The present invention relates to the construction industry, and more particularly to clamping means for a device for driving flexible rods in soil.
The invention may be used for driving elongate rod-shaped elements in soil. The use of this invention is most advantageous for driving rod-shaped elements having a low longitudinal rigidity, such as ground electrodes, anchors, filter tubes and the like.
The volume of work associated with driving rod-shaped elements in soil in industrialized countries is very important and is increasing.
Thus a problem arises of providing special devices for driving rod-shaped elements in soil and development of clamping means for transmitting forces from the driving device to the element being driven.
In driving rod-shaped elements of a considerable longitudinal rigidity, a driving device is mounted on the upper end face of the element being driven. This method is unsuitable for driving rod-shaped elements having a low longitudinal rigidity since the rod-shaped element may loose its stability and be deformed under the action of driving load.
In order to perform the driving process, rods having low longitudinal rigidity are cut into portions, each portion being of a length permitting the driving to be made with the action of driving load on the upper end face thereof without a loss of stability and, as the driving proceeds, these portions are connected to one another, to obtain a required length, by welding, using threaded or other couplings. This increases labour-consumption of the driving process and prolongs the driving time.
At present there is known a clamping means for a device for driving ground electrodes and like elements in soil (cf. USSR Inventor's Certificate No. 248553, E 02 D 7/20) comprising a casing provided with an open-ended tapered inner space accommodating wedging elements and a spring ensuring the engagement of the wedging elements with the casing and rod being driven. The known clamping means is used in combination with a hydraulic power cylinder which is fastened by means of collars to an electric transmission line tower and forces the rod deep into soil when fluid is fed to the upper chamber of the hydraulic cylinder and repositions the clamping means when the fluid is fed to the lower chamber of the cylinder.
The known clamping means ensures clamping of the driven rod when a force acting from the top is applied to the casing. This force is developed due to feeding of fluid to the upper chamber of the driving hydraulic cylinder. A reaction force which thus appears is directed towards lifting the casing of the hydraulic cylinder. In order that such movement could not take place, the casing of the hydraulic cylinder is fixedly connected to the electric transmission line tower which takes up the reaction force. When the clamping means approaches the soil surface, the rod clamped by the wedging elements should be released, and the clamping means should be moved up along the rod at a certain height to perform the next driving cycle. For that purpose, fluid is fed to the lower chamber of the hydraulic cylinder. Thus the piston of the hydraulic cylinder moves up and entrains with it the casing of the clamping means. The wedging elements move apart and release the rod. The rod is prevented from lifting by the forces of cohesion with the soil, and the clamping means moves along the rod.
When the piston attains the utmost position, the fluid is fed to the upper chamber of the hydraulic cylinder. The piston starts moving down. The clamping means jams the rod, and the driving continues.
Therefore, the prior art clamping means enables a static forcing of the rod deep into soil, and requires a force for releasing the rod to be applied from the bottom up, which force is developed when fluid is fed to the lower chamber of the hydraulic cylinder.
The disadvantage of the known clamping means consists in that it cannot be used for driving rods with the employment of vibratory or impact mechanisms since reactive forces occurring during operation of such mechanisms cannot ensure the release of the rod as they are very small.
Also known in the art is a clamping means for a device for driving elongate rod-shaped elements in soil (cf. USSR Inventor's Certificate No. 279450, E 20 D 9/02) comprising a casing, a lifting gear and a vibrator mounted in the upper portion of the device. The casing of the clamping means accommodates two tapered sleeves having the smaller bases of their tapering inner spaces facing each other. The tapering inner spaces of the tapered sleeves accommodate spring-biased wedging elements in the form of balls separated by means of two cages: an upper cage and a lower cage. The upper cage is connected by means of a pin to one end of a rocker arm having the other end provided with sockets in which there are fixed springs and to which there is connected a rope of the lifting gear.
When suspended the vibrator, with the clamping means fixed thereto, is supported with the rocker arms on weights fastened to the ropes. The springs are compressed by the amount of the rocker arm stroke, and the upper cage and the balls of the upper tapered sleeve are lifted so that the clamping means is released. The rod is passed through the hole of the vibrator, and the clamping means is lowered until it bears against the soil. When the tension from the lifting ropes is released, the rod is clamped under the action of gravity of vibrator and under the action of the springs urging the balls against the rod. Thus, the balls of the lower tapered sleeve take up and transmit to the rod the driving force, and the balls of the upper sleeve take up the reactive force from the vibrator and prevent the entire clamping means from lowering or lifting, respectively, along the rod. Upon switching the vibrator on, the driving of the rod begins. When the clamping means approaches the soil surface, to release the rod being driven and to re-position the vibrator and the clamping means to a height anew, the lifting gear is put on. The rocker arms displace the upper cage and release the rod.
The disadvantages of the prior art clamping means consist in the use of two tapered sleeves and self-wedging devices each consisting of the tapered sleeve, cage and balls, which makes the construction complicated, in heavy weight and large size of the clamping means, as well as in the need to employ a lifting gear for the release of the rod and re-positioning of the driving device therealong.
Known in the art is also a clamping means for a device for driving earthing electrodes in soil (cf. USSR Inventor's Certificate No. 376525, E 02 D 7/18) comprising a casing having an open-ended tapered inner space, which is made integral with a movable spring-biased anvil. Wedging elements and a spring ensuring their engagement with the casing of the clamping means and with the rod are accommodated in the inner space of the clamping means. The driving device comprises an impact device suspended to a base tractor. An auxiliary holder is mounted on the impact device co-axially with the main clamping means. The rod is passed through the holder and the clamping means until it bears against the soil. A hammer piston of the impact device imparts a blow to the movable anvil. The clamping means will then clamp the rod and move together therewith downwards. Concurrently with the driving of the rod, the return spring is compressed. When the hammer piston moves back upwards for imparting the next blow, the return spring lifts the anvil with the clamping device back into the initial position.
The disadvantages of the prior art clamping means consist in insufficient strength of the movable anvil of the device which is integral with the casing of the clamping means and takes up an off-set impact load, hence in low reliability and short service life.